Conveyance systems ordinarily rely on friction drives (i.e., belts or rollers) using gravity as a friction force to maintain an article being conveyed along a transfer path. However, when the article being transported is relatively flat and/or lightweight, ambient air streams can cause the article to get blown off from the conveyor. Additionally, when the conveyor is vertical or inclined, the article is likewise susceptible to sliding, rolling or flying away from the transfer path.
U.S. Pat. No. 5,671,920 describes use of an external low pressure generator for providing an additional force to maintain an article on a conveyor.
U.S. Patent Application Publication No. 2005/0133980 describes use of an axial fan on the opposite side of a belt from paper being conveyed thereon.
U.S. Pat. No. 6,565,321 describes a vortex attractor. An impeller including a plurality of radial blades extending in a direction of the rotation axis are provided to generate a vortex flow. The vortex flow provides a central negative low pressure region which can be used to attract an object or maintain the vortex attractor against or at a distance from a surface.